Multiple radio base station networks have been developed to overcome a variety of problems with single radio base station networks such as spanning physical radio wave penetration barriers, wasted transmission power by portable computing devices, etc. However, multiple radio base station networks have their own inherent problems. For example, in a multiple base station network employing a single shared channel, each base station transmission is prone to collision with neighboring base station transmissions in the overlapping coverage areas between the base stations. Therefore, it often proves undesirable for each base station to use a single or common communication channel.
In contradistinction, to facilitate the roaming of portable or mobile devices from one coverage area to another, use of a common communication channel for all of the base stations is convenient. A roaming device may easily move between coverage areas without loss of connectivity to the network.
Such exemplary competing commonality factors have resulted in tradeoff decisions in network design. These factors become even more significant when implementing a frequency hopping spread spectrum network. Frequency hopping is a desirable transmission technique because of its ability to combat frequency selective fading, avoid narrowband interference, and provide multiple communications channels.
Again, however, changing operating parameters between coverage areas creates difficulties for the roaming devices which move therebetween. In particular, when different communication parameters are used, a portable or mobile device roaming into a new base station coverage area is not able to communicate with the new base station without obtaining and synchronizing to the new parameters. This causes communication backlog in the network.
Moreover, even when a radio frequency network is established to cover the premises of a building or group of buildings, certain types of communication flow between certain types of devices make for inefficient use of such a network. In fact, an ordinarily efficient network configuration may be deemed intolerable in certain communication scenarios.
Computer terminals and peripheral devices are widely used. Many types of computer terminals exist which vary greatly in terms of function, power and speed. Many different types of peripheral devices also exist, such as printers, modems, graphics scanners, text scanners, code readers, magnetic card readers, external monitors, voice command interfaces, external storage devices, and so on.
Computer terminals have become dramatically smaller and more portable, as, for example, lap top computers and notebook computers. Computer terminals exist which are small enough to be mounted in a vehicle such as a delivery truck or on a fork lift. Hand held computer terminals exist which a user can carry in one hand and operate with the other.
Typical computer terminals must physically interface with peripheral devices. Thus, there must either be a cable running from the computer terminal to each peripheral device, or the computer terminal must be docked with the device while information transfer takes place.
In an office or work place setting, the physical connection is typically done with cables. These cables pose several problems. For example, many cables are required in order for a computer terminal to accommodate many peripheral devices. In addition, placement of peripheral devices is limited by cable lengths. While longer cables may be used, they are costly. Additionally, there may be a limited number of ports on a computer terminal, thus limiting the number of peripherals that may be attached.
Another problem arises when several computer terminals must share the same peripheral device, such as a printer. All of the computers must be hardwired to the printer, which may create a protocol problem if the computer terminals are of different types.
Peripheral cabling is an even greater problem in scenarios where hand-held and portable computer terminals are used. The cabling required for an operator to carry a hand-held computer terminal in one hand, have a small portable printer attached to his belt, and carry a code reader in the other hand is cumbersome and potentially even dangerous. For example, such an operator loses a great deal of mobility and flexibility while supporting a number of cabled devices. In addition, as cables wear out and break, exposed electric current could shock the operator, or create a spark and potentially cause a fire or explosion in some work areas.
The requirement of physically connecting the computer terminals and peripherals severely reduces the efficiency gained by making the devices smaller. An operator must somehow account for all of the devices in a system and keep them all connected. This can be very inconvenient. For example, an operator having a notebook computer and a modem in a briefcase may wish to have the freedom to move around with the computer but without the modem. He may, for example, wish to work at various locations on a job sight and at various times transmit or receive information via his modem. If the modem and the computer are hard wired together, he must either carry the modem with him or keep connecting and disconnecting it.
Furthermore, cabling can be expensive because cables frequently prove to be unreliable and must be replaced frequently. In portable environments, cables are subject to frequent handling, temperature extremes, dropping and other physical trauma. It is not uncommon for the cables or the connectors for the cables on the devices to need replacing every three months or so.
Attempts to alleviate or eliminate these problems have been made but have not been entirely successful. One solution is to incorporate a computer terminal and all of the peripherals into one unit. However, this solution proves unsatisfactory for several reasons. For example, the incorporation of many devices into one unit greatly increases the size and weight of the unit, thus jeopardizing its portability. Furthermore, incorporating all of the functions into one unit greatly reduces and, in most cases eliminates, the flexibility of the overall system. A user may only wish to use a hand-held computer terminal at times, but at other times may also need to use a printer or occasionally a code reader. An all-incorporated unit thus becomes either overly large because it must include everything, or very limiting because it does not include everything.
Another solution has been to set up Local Area Networks (LAN's) utilizing various forms of RF (Radio Frequency) communication. The LAN's to date, however, have been designed for large scale wireless communications between several portable computer terminals and a host computer. Therein, the host computer, itself generally a stationary device, manages a series of stationary peripherals that, upon requests to the host, may be utilized by the portable terminals. Other large scale wireless communications have also been developed which provide for RF communication between several computer terminals and peripheral devices, but have proven to be ineffective as an overall solution. For example, these systems require the peripheral devices to remain active at all times to listen for an occasional communication. Although this requirement may be acceptable for stationary peripheral devices receiving virtually unlimited power (i.e., when plugged into an AC outlet), it proves detrimental to portable peripherals by unnecessarily draining battery power. Similarly, in such systems, the computer terminals are also required to remain active to receive an occasional communication not only from the other terminals or the host, but also from the peripherals. Again, often unnecessarily, battery power is wasted.
In addition, such large scale systems are designed for long range RF communication and often require either a licensed frequency or must be operated using spread spectrum technology. Radios in such systems are typically cost prohibitive, prove too large for convenient use with personal computers and small peripheral devices, and require a great deal of transmission energy utilization.
Furthermore, these systems do not provide for efficient communication between portable computer devices and peripherals. For example, a portable computer device may be mounted in a delivery truck and a driver may desire to transmit data to, or receive data from, a host computer or peripheral device at a remote warehouse location. While permitting such transmission, such wide area networks (WANs) only provide point-to-point communications, use a narrow bandwidth, and often have heavy communication traffic. As a result, WANs are generally slow and expensive and simply do not provide an effective overall solution.
Additionally, in order for a computer device to be effectively portable in these systems, it must be capable of participating on any number of LANs operating with different communication parameters and protocols. Thus, each portable computer device requires a plurality of built-in radio transceivers, one to accommodate each of such LANs. As a result, portable computer devices can become costly, excessively large, heavy, and power hungry.
A further source of inefficiency in a LAN environment is periodic interference, attributable to microwave ovens or other sources. A standard interference avoidance protocol can detect periodic interference as it occurs, through Received Signal Strength Indicator (RSSI) and error rate monitoring, but a standard protocol system cannot predict the future timing of a periodic interference signal.
Thus, there is a need for a radio frequency communication system and associated protocol that monitors RSSI and error rates to detect the presence of interference, and which additionally can detect when such interference is periodic in nature, so that the system can predict the future timing of the periodic interference and optimize communication procedures on the basis of such a prediction.
An object of the invention is to provide a radio frequency communication system that detects interference, and determines whether such interference is periodic in nature.
Another object of the invention is to provide a radio frequency communication system that detects interference and determines whether it is periodic in nature by monitoring RSSI and error rates.
A further object of the invention is to provide a radio frequency communication system that responds to a periodic interference signal by optimizing communication procedures based on a prediction of the future timing of such a periodic interference signal.